Guillermo Bustos-Pérez\(^{1,2,3}\)
Brad Gravina\(^{4,5}\)
Michel Brenet\(^{5,6}\)
Francesca Romagnoli\(^1\)
\(^1\)Universidad Autónoma de Madrid. Departamento de Prehistoria y Arqueología, Campus de Cantoblanco, 28049 Madrid, Spain
\(^2\)Institut Català de Paleoecologia Humana i Evolució Social (IPHES), Zona Educacional 4, Campus Sescelades URV (Edifici W3), 43007 Tarragona, Spain
\(^3\)Àrea de Prehistoria, Universitat Rovira i Virgili (URV), Avinguda de Catalunya 35, 43002 Tarragona, Spain
\(^4\)Musée national de Préhistoire, MCC, 1 rue du Musée, 24260 Les Eyzies de Tayac, France
\(^5\)UMR-5199 PACEA, Université de Bordeaux, Bâtiment B8, Allée Geoffroy Saint Hilaire, CS 50023, 33615 PESSAC CEDEX, France
\(^6\)INRAP Grand Sud-Ouest, Centre mixte de recherches archéologiques, Domaine de Campagne, 242460 Campagne, France
Corresponding authors:
G.B.P. guillermo.willbustos@mail.com
F.R. f.romagnoli2@gmail.com
Backed flakes (core edge flakes and pseudo-Levallois points) represent special products of Middle Paleolithic centripetal flaking strategies. Their peculiarities are due to their roles as both a technological objective and in the management of core convexities to retain its geometric properties during reduction. In Middle Paleolithic contexts, these backed implements are commonly produced during Levallois and discoidal reduction sequences. Backed products from Levallois and discoidal reduction sequences often show common geometric and morphological features that complicate their attribution to one of these methods. This study examines the identification of experimentally produced discoidal and recurrent centripetal Levallois backed products (including all stages of reduction) based on their morphological features. 3D geometric morphometrics are employed to quantify morphological variability among the experimental sample. Dimensionality reduction though principal component analysis is combined with 11 machine learning models for the identification of knapping methods. A supported vector machine with polynomial kernel has been identified as the best model (with a general accuracy of 0.76 and an area under the curve [AUC] of 0.8). This indicates that combining geometric morphometrics, principal component analysis, and machine learning models succeeds in capturing the morphological differences of backed products according to the knapping method.
Key words: lithic analysis; Levallois; Discoid; Geometric Morphometrics; Machine Learning; Deep Learning
The Middle Paleolithic in Western Europe is characterized by the diversification and increase of knapping methods resulting in flake-dominated assemblages (Delagnes and Meignen, 2006; Kuhn, 2013). Discoidal and the recurrent centripetal Levallois are two of the most common flake production systems during this period. Following Boëda (1995a, 1994, 1993), there are six technological criteria that define discoidal debitage:
In addition, according to Boëda (1994, 1993) six characteristics define the Levallois knapping strategy:
Depending on the organization of the debitage surface Levallois cores are usually classified into preferential method (were a single predetermined Levallois flake is obtained from the debitage surface) or recurrent methods (were several predetermined flakes are produced from the debitage surface) with removals being either unidirectional, bidirectional or centripetal (Boëda, 1995a; Delagnes, 1995; Delagnes and Meignen, 2006).
Examples of backed flakes categories with key features discussed in the present research)
Both knapping methods involve the removal of backed products that usually comprise two categories: core edge flakes (eclat débordant) and pseudo-Levallois points.
Core edge flakes / eclat débordant (Beyries and Boëda, 1983; Boëda, 1993; Boëda et al., 1990) are technical backed knives that have a cutting edge opposite and parallel (or sub-parallel) to an abrupt margin (a back that usually has an angle close to 90º). This back commonly results from the removal of one of the lateral edges of the core and can be plain, retain the scars from previous removals, be cortical, or a combination of these attributes. Core edge flakes are also divided into two categories: “classic core edge flakes” and “core edge flakes with a limited back.” “Classic core edge flakes” (Beyries and Boëda, 1983; Boëda, 1993; Boëda et al., 1990), which are sometimes referred to as “core edge flakes with a non-limited back”/“éclat débordant à dos non limité” (Duran, 2005; Duran and Soler, 2006), have a morphological axis more or less similar to the axis of percussion. “Core edge flakes with a limited back”/“éclat débordant à dos limité” a offset axis of symmetry in relation to the axis of percussion (Meignen, 1996; Meignen, 1993; Pasty et al., 2004). This orientation often leads to the back not being parallel to nor spanning the entire length of the sharp edge or the percussion axis (Slimak, 2003).
Pseudo-Levallois points (Boëda, 1993; Boëda et al., 1990; Bordes, 1961, 1953; Slimak, 2003) are backed products where the edge opposite to the back has a triangular morphology. This triangular morphology is usually the result of the convergence of two or more scars. As with core edge flakes, the back usually results from the removal of one of the lateral edges of the core and can be plain, retain the scars from previous removals, or more rarely be cortical or a combination of these traits. Both pseudo-Levallois points and core edge flakes with a limited back share a symmetry offset from the axis of percussion but are clearly differentiable due to their morphology. The present study includes the three categories defined above as backed products.
Depending on the knapping method, different roles in Levallois recurrent centripetal and discoidal debitage are attributed to core edge flakes and pseudo-Levallois points. Boëda et al. (1990) focus on the role of core edge flakes and cortically backed flakes for maintaining the lateral convexities throughout Levallois recurrent centripetal reduction. Similarly, pseudo-Levallois points contribute to maintaining the lateral and distal convexities between different series of removals (Boëda et al., 1990).
Focusing on the variability of discoidal debitage, Slimak (2003) noted that pseudo-Levallois points are short products that induce a limited lowering of the core overhang (the intersection between the striking and debitage surfaces). In contrast, core edge flakes can result from several distinct production objectives. Expanding on the roles of pseudo-Levallois points and core edge flakes within discoidal debitage, Locht (2003) demonstrated the systematic production of both products at the site of Beauvais. This indicates that at Beauvais, core edge flakes and pseudo-Levallois points were the main predetermining/predetermined products (Locht, 2003).